Sequence and secondary structure of the rDNA second internal transcribed spacer in the sibling species Culex pipiens L. and Cx. quinquefasciatus Say (Diptera: Culicidae).

The primary and secondary structure of the second internal transcribed spacer (ITS2) of ribosomal DNA (rDNA) of two members of the Cx. pipiens complex, Cx. pipiens and Cx, quinquefasciatus, were examined in order to better understand the relationships between these two sibling mosquito species. The length of the sequenced rDNA fragments was 512 bp (Cx. pipiens) and 513 bp (Cx. quinquefasciatus), including the ITS2 regions and flanking 5.8S-28S coding regions. The ITS2 sequences of Cx. pipiens and Cx. quinquefasciatus were 297 and 298 bp in length respectively and showed a 97% identity. In fact, they had identical G+C content (58%) and the only differences observed are six mismatches (three transitions/three transversions), six single-base and one triple-base deletions/ insertions. The observed ITS2 secondary structures of Cx. pipiens and Cx. quinquefasciatus were very similar. Furthermore, the ITS2 sequences of specimens belonging to three populations of Cx. pipiens from Italy and four populations of Cx. quinquefasciatus (three from Africa and one from North America) were analysed in order to detect the presence of potential species-specific diagnostic restriction sites.